Gellan gum microgels as effective agents for a rapid cleaning of paper

Microgel particles have emerged in the last few years as a favourite model system for fundamental science and for innovative applications ranging from industrial to biomedical fields. Despite their potentialities, no works so far have focused on the application of microgels for cultural heritage preservation. Here we show their first use for this purpose, focusing on wet paper cleaning. Exploiting their retentive properties, microgels are able to clean paper ensuring more controlled water releasing from the gel matrix, in analogy to their macroscopic counterpart, i.e., hydrogels. However, differently from these, the reduced size of microgels makes them suitable to efficiently penetrate in the porous structure of the paper and to easily adapt to the irregular surfaces of artefacts. To test their cleaning abilities, we prepare microgels made of Gellan gum, a natural and widespread material already used as a hydrogel for paper cleaning, and apply them to modern and ancient paper samples. Combining several diagnostic methods, we show that microgels performances in the removal of cellulose degradation by-products for ancient samples are superior to commonly employed hydrogels and water bath treatments. This is due to the composition and morphology of ancient paper, which facilitates microgels penetration. For modern paper cleaning performances are at least comparable to the other methods. In all cases, the application of microgels takes place on a time scale of a few minutes, opening the way for widespread use as a rapid and efficient cleaning protocol.